Propeller Diameter Difference and Its Impact on Propulsion Performance on Actual Sea Conditions

Propeller design is a significant process that is overlooked in many design situations. Using propeller vortex lifting line code and two-dimensional analysis with Brockett diagrams, a propeller design can be optimized for an Autonomous Underwater Vehicle with a given design speed by varying blade number, propeller diameter, hub position, and chordlength distribution over a given range of RPS appropriate to the AUV's thrusters [1]. Initial design decisions from PVL code chose a three-bladed 0.625m diameter propeller at 2RPS, with a hub located at r/R(0.2) and an efficiency of 0.7091. Final propeller design modified the chord distribution to improve distributed lift coefficients and to ensure that shallow-water operations would not experience cavitation effects. The final design geometry used the same values of the propeller blade number, diameter, RPS and hub location as the initial design, but at an efficiency of 0.7642. While off-the-shelf propellers, such as those designed for model airplanes, can have high calculated efficiencies relative to actuator disk theory, the lift coefficient at each radial position and the resulting stalling effects must be considered. Comparison of an existing design with an optimized design improves existing propellers and contributes to the process of choosing future off-the-shelf propellers.

Classical methods of ship propulsion estimations based on the traditionally applied system of hull and propeller interaction coefficients are not suitable for prediction of icebreaker performance in ice. This is because the wake fraction tends to assume negative values in operating conditions typical of navigation in ice. This paper suggests an alternative system of hull/propeller interaction coefficients to overcome the problem. The alternative system comprises the thrust deduction factor t and the factors allowing for hull effect on thrust iTB and hull effect on torque iQB. An alternative method of ship propulsion performance estimations is developed based on this system of coefficients to take into account all characteristics of icebreaker sailing in ice. The method was used to analyze the full-scale data obtained from sea trials of the icebreakers Vladivostok and Novorosiisk. The initial data inputs for the analysis were ship speed in ice and consumed power measured during the sea trials. The number of propeller revolutions and ice resistance were calculated. The estimated propeller revolutions were compared with the full-scale data gathered during the sea trials in ice. The ice resistance was compared with the predictions based on model tests in ice basin. It is shown that at slow speeds in ice, ranging from 0.5 to 5.0 knots, the predicted number of propeller revolutions is in good agreement with the data measured during the sea trials. Propulsion performance of the Vladivostok icebreaker in 1.5-m thick ice was estimated

A novel dual-impact horizontal rotor wave energy converter (DHRWEC) system was designed to accommodate the short wave periods and low wave heights that are typical of China’s coastal regions, based on a combination of wave concentration and amplification technology with a four-point catenary mooring system. This study investigates the stability and survivability of the DHRWEC system under actual sea conditions. Numerical simulations and experimental validations are conducted to assess the performance of the system. The results indicate that if even one anchor chain fails under extreme conditions, the safety factor of the remaining chain’s maximum mooring force exceeds three, meaning that it meets international safety standards. The maximum surge and sway displacements are found to be 5.5 m and 3.0 m, respectively, values that align well with predictions from simulations and which confirm stable operation in the designated position. No risk of capsizing is detected, indicating that the system is robust in real sea environments. Sea trials also confirm reliable startup and give an energy conversion efficiency of about 21.33%. These findings offer valuable insights for the development of similar technologies, and provide a solid foundation for the practical application and sustained operation of the system.

Numerical assessment of the scale effects on the propulsive performance of a ship with gate rudder system

This paper describes a thoroughly integrated design procedure and an example of its application, carried out in order to define the propeller of a twin screw fast ship. As particular attention had to be paid to fulfil many contractual requirements, such as the propulsion efficiency, cavitation and related phenomenal pressures induced on the hull vibrations and noise, both lifting line and surface effect theories for the propeller design and behaviour prediction were employed. A wide program of model tests was carried out for checking· and optimizing the propeller design, so that propulsion, cavitation and noise aspects were investigated. Then a full scale optimization program was planned and carried out in order to ascertain the expected differences between model and full scale propellers behaviour. As a final step, the optimum full scale propeller was developed and submitted to a complete experimental test program, thus obtaining all necessary data for comparing theoretically predicted, model and full scaly propeller behavior. All results deduced from the abovementioned program steps are presented and discussed in the paper where a brief description of theoretical and experimental methodologies is also given.

Boundary Layer Ingestion is one of the most trending applications in the aircraft propulsion field. Here, it is applied on a small unmanned aerial vehicle wing to investigate its advantages and disadvantages in terms of lift, drag, power consumption, and propulsive efficiency. To do so, a parametric study is conducted to quantify how these parameters change when the propeller diameter and its horizontal and vertical positions vary.

This study aims to enhance the performance and safety of small waterjet propulsion systems for outboard motors. A numerical simulation approach was employed to analyze the effects of guide vane quantity, nozzle attack angle, and inner flow channel geometry on propulsion performance and cavitation resistance. The results indicate that the number of guide vanes exhibits minimal influence on hydrodynamic performance. As the number of guide vanes increases, the declines in head, thrust, and propulsion efficiency remain marginal. Consequently, moderately increasing the number of guide vanes can improve the operational safety and stability of the waterjet propulsion system with only minor performance trade-offs. Within the investigated attack angle range (0°–15°), the straight-tube channel demonstrates superior hydrodynamic performance compared to the divergent channel, with the most pronounced advantages observed at a 10° attack angle. Specifically, the hydraulic head, thrust, and propulsion efficiency increase by 6.62%, 6.53%, and 4.45%, respectively, under this configuration. In contrast, the divergent-channel design shows slightly enhanced cavitation resistance but requires compromising propulsion performance. For both channel types, the propulsion efficiency initially increases and then decreases with rising attack angles, while the average cavitation value gradually decreases. At a 10° attack angle, the average cavitation value is smaller, and propulsion efficiency improves by more than 15% compared to 0°. Therefore, by setting an appropriate nozzle attack angle, it is possible to significantly enhance both propulsion efficiency and cavitation resistance. Taking both hydrodynamic performance and cavitation resistance into account, the optimal configuration involves a straight-tube flow channel with 3–5 guide vanes, a vane thickness of 7 mm, and a 10° nozzle attack angle.

High fidelity numerical simulation of airfoil thickness and kinematics effects on flapping airfoil propulsion

Uncertainty analysis of speed–power performance based on measured raw data in sea trials

Ever increasing fuel prices and environmental concerns are forcing commercial vessel operators and designers to re-assess current vessel designs with an emphasis on their propulsion systems. The most important parameter determining propulsive efficiency is the diameter of propeller. Many investigations have been carried out to adapt a large and slow turning propeller known as one of the most robust and effective way of achieving high efficiency in ship propulsion system. However, for the same vessel a further increase of propeller diameter would require the modification of the aft end while still paying attention to the hull clearance to prevent excessive propeller excited vibrations. In order to take the advantage of this approach small workboats (e.g. tug boats, fishing vessels etc.) operate in service with a significant increase of aft draught and hence resulting "inclined keel" configuration can be observed. Although it is not unusual to see large vessels sometimes to operate with stern trim to improve their operational performance and fuel efficiency, it is rare to see a such vessel purposely built with an inclined keel feature to fit a large diameter propeller for power saving. This paper investigates the application of the inclined keel configuration to a 3600TEU container vessel with the aim of fitting an 11 % larger diameter propeller (and hence resulting 17.5 % lower rpm) to gain further power saving over the similar size basis container ship with conventional "level keel" configuration.

The traditional laboratory models for the hydroelasticity and seakeeping performance of ships are tested in calm water and in uni-directional, artificially generated waves. A new alternative to the tank model measurement methodology is to conduct experiments using large-scale models in actual sea conditions. To implement the tests, a large-scale segmented self-propelling model and testing system were designed and assembled. A buoy wave meter was adopted to record the coastal waves that the model encountered during the tests. The analysis of the results of waves in sheltered waters by the spectral method shows good agreement with ISSC spectra. To investigate the difference between this new methodology and the traditional towing tank tests, a small-scale model, whose type and configuration are the same as those of the large-scale model ship, was used and tests were conducted in a towing tank. Comparison of the two experimental results shows that there is a remarkable difference in the response characteristics between the large-scale model at sea and the small-scale model in the tank. Numerical simulations of the responses of the ship under equivalent sea states were also carried out. The influence of directional spreading functions on the results was analyzed by a numerical approach. The classical model tests under long-crested waves in the towing tank over-estimate the motion and wave load responses; however, large-scale model tests carried out at sea are more reasonable for ship design and scientific research.

This paper addresses the challenges and advances made in the hydrodynamic design and design evaluation of ducted propellers. The application of new ducted propeller analysis tools is shown for the practical case of the design of controllable pitch propellers for hopper dredgers. Results of model tests and sea trials are compared with results of a state-of-the-art boundary element method (BEM) code that is used for the simulation of the unsteady cavitating flow around ducted propellers. The results of the BEM simulations are compared to more time consuming and comprehensive URANS sliding interface calculation results in which the flow including the unsteady flow around the rotating propeller is modelled in the RANS domain. Comparisons are made of pressure distributions and pressure side cavitation margins that are important in the propeller blade design. The details of the flow into the duct are discussed as well as its implications on the propeller blade design. The employed BEM method is proposed as the best practical next step in ducted propeller design given its reasonable calculation times. Based on the obtained results a new research initiative has been started to obtain better sea trial data from ducted propellers to improve and validate the ducted BEM method as well as the SI URANS method.

An accurate estimation of ship speed loss is required to verify ship propulsion performance in actual sea conditions. In this study, ship speed loss was estimated using a neural network. Firstly, the directional spectra were extracted from the ocean wave hindcast database of Japan Weather Association. Then, the spectra were converted into wave spectra of encounter. Secondly, ship speed through water was modeled using ship monitoring data and spectra with a neural network. Thirdly, speed-power curves were estimated using the model. Effects of the wind and waves on ship speed were checked by considering the sensitivity of the model's outputs. Finally, ship speed loss was calculated using this model. The estimated ship speed loss was consistent with the ship speed loss obtained using ship monitoring data.

A numerical study on self-propulsion performance of the 66k DWT bulk carrier in low-speed calm water and regular wave conditions

This study explores the effects of complex driving motion on the propulsion performance of a flexible foil heaving in the flight regimes of natural flyers. Such a fluid-structure interaction problem is numerically studied using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. It is found that, at the Reynolds number 200 and when the foil’s bending stiffness and mass ratio are moderate, adding an extra driving motion of doubled frequency to a purely harmonic motion on the foil’s leading edge can enhance the thrust and propulsive efficiency by about 860% and 70%, respectively. The improvement in thrust increases with the extra-driving-motion amplitude. When the extra-driving-motion amplitude is fixed, there exists an optimal extra-driving-motion phase angle. As the foil becomes much stiffer or lighter, the improvement in the propulsion performance turns less. On the other hand, as the foil becomes much more flexible or heavier, drag instead of thrust is generated, and extra driving motion brings no improvement. Although the extra driving motion can improve the foil’s propulsion performance in flows of different Reynolds numbers, the increasing rate of the thrust reduces with the Reynolds number. Through this study, details about the competitions among various forces exerted on the foil and their roles in the foil’s dynamics are also revealed.